Heretofore, the opening and closing of windows has been based selectively on either the swing system or the slide system. Particularly in high-rise buildings, windows are constructed so that they cannot be opened beyond a certain degree to prevent falling. Such construction has a problem that sufficient ventilation is impossible.
Thus, a multiple window such as the one disclosed in Japanese Utility Model Application Laid-Open No. 69533/1974 is known. The multiple window disclosed therein comprises two windows, upper and lower, connected together and adapted to be opened and closed by being bent along the connecting portion by means of hinges, the arrangement being such that when the two windows are bent for opening, the upper end of the upper window slides down along guides formed in the opposite lateral frames of a window attaching framework.
When the multiple window disclosed in Japanese Utility Model Application Laid-Open No. 69533/1974 is opened, the upper end of the upper window moves downward, whereby openings for ventilation are defined in the opposite lateral regions of the upper and lower windows and in the region above the upper window. When the upper end of the upper window moves downward, the upper end of the upper window hits the lower end portions of the guides with a shock owing to the weight of the upper window, often resulting in earlier wear or damage to both. Further, when the upper and lower windows are to be closed, a force is required to raise the upper window, making it necessary to close with a heavy force.